Counting accelerometers have heretofore been provided of the mechanical type. In general, they consisted of a cylindrical mass which was yieldably retained in the center of a cylinder. The cylinder was sized to permit the mass to travel longitudinally of the cylinder. The cylinder carried contacts which were adjustable and which were adapted to be physically engaged by the mass at various load levels. Since such a counting accelerometer was substantially mechanical in operation, it had various undesirable features. For example, it would malfunction under vibration. In addition, its useful service life was limited to such an extent because of wear and other factors that it has not been particularly feasible to utilize counting accelerometers of this type. There is, therefore, a need for a new and improved counting accelerometer.
In connection with counting accelerometers, it has been found that measuring acceleration does not give an exact correlation to the degree of stress which has been encountered by an aircraft. This is because the degree of stress is related to the gross weight of the aircraft which may change because of the bomb load or the fuel load carried by the aircraft. To precisely measure the true stress, it is necessary to know the gross weight of the aircraft at the time that acceleration is being measured by a counting accelerometer. Therefore, there is a need for means other than a counting accelerometer for precisely measuring stress levels encountered by an aircraft.